1. Field of the Invention
The present invention relates to a shroud contact wear sensor in a turbo machine, such as the compressor or turbine of a jet engine, for use in measuring the amount of wear due to contact of a shroud between rotor blades and the shroud while the compressor or turbine is being operated.
2. Description of the Prior Art
A conventional device for measuring the clearance between the tip of rotor blades and a shroud in a turbo machine includes, as shown in FIG. 4, a clearance sensor 21 fixed to a shroud 22 which is disposed in a casing 23.
In a region where the shroud 22 is close to the rotor blades 25, a wearable portion 24 is provided because the shroud 22 may become worn by contact with the rotor blades 25 during operation. The clearance sensor 21 measures a clearance C.sub.1 instead of the true clearance C, and the true clearance C is calculated by subtracting an initial thickness T of the wearable portion 24 from the clearance C.sub.1, in accordance with the equation C=C.sub.1 -T.
When the rotor blades contact the shroud during the operation of the turbo machine both the tip of the rotor blades and the wearable portion of the shroud are worn. It is possible, in the apparatus of the prior art, to measure an increase in clearance at the tip of the rotor blades caused by their wear, but it is impossible to measure an increase in the clearance caused by wearing of the shroud.